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PRO Arm canister combinations


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#1 Jerry Franck

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Posted 14 May 2010 - 06:43 PM

PRO Arm Users,

I have a question about canisters and using different combinations for different payloads.

Ever since I've had my arm (=6 months) I've only once mixed blues and blacks. I mostly live on the 4 blue combination as I've found this handles most of the jobs I do.

But recently, I discovered that on a light setup I have better results with only two blacks (at 90% crancked out) than 4 blues all the way down-crancked...?
I noticed that the rig actually lands at the spots I want it to, easier than with the 4 blues. Why is that?
The 4 blues seem more "jerky" than the "stiff, precise" feel of the blacks.

What combinations do you prefer for what setups?
So, any input from veterans on this topic would be greatly appreciated...

Thanks,
Jerry
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#2 Mike McGowan SOC

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Posted 14 May 2010 - 09:48 PM

i cant say that my advice is correct, just that it works for me. that being said.................

i generally use 2 blacks and 2 blues. i have the blacks in the upper top half and the lower bottom half (this way i can easily adjust the blues while im wearing the rig).

i also find that (particularly with the wide variety of cameras being used these days D5 to arri cam's) i switch my springs a lot. i rarely use 4 blacks (lucky me) and i occasionally use only 2 blues (like for a D5). 2 and 2 seems to be the best combination for me.

ive also noticed that (and again, im not joe tec so take this with a grain of salt) pretty much anything i try on the pro arm works. it just rolls with the punches.

in summary, id say, if it works us it. maybe somebody techie will come on and let you know how your supposed to do it.

my 2 cents.
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#3 Matt Petrosky

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Posted 16 May 2010 - 12:05 PM

...i have the blacks in the upper top half and the lower bottom half (this way i can easily adjust the blues while im wearing the rig).


Funny Mike, I do the opposite, I put the blacks in the lower top half and the upper bottom half. This way I can easily adjust the black canisters while wearing the rig. I like this because it allows me to make adjustments faster because it takes many less turns on the black canisters then the blue canisters to accomplish the same spring tension change. I think I picked this up from Andrew or Chris, but this is one of the great things about the PRO arm--it's versatility.

Hope you are sunny and warm in South Florida, it's been cold and rainy on this Michigan job.

-Matt
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#4 Alec Jarnagin SOC

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Posted 16 May 2010 - 12:50 PM

" I put the blacks in the lower top half and the upper bottom half. This way I can easily adjust the black canisters while wearing the rig. I like this because it allows me to make adjustments faster because it takes many less turns on the black canisters then the blue canisters to accomplish the same spring tension change. "

Ditto.
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#5 Jerry Franck

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Posted 16 May 2010 - 03:54 PM

...i have the blacks in the upper top half and the lower bottom half (this way i can easily adjust the blues while im wearing the rig).


Funny Mike, I do the opposite, I put the blacks in the lower top half and the upper bottom half. This way I can easily adjust the black canisters while wearing the rig. I like this because it allows me to make adjustments faster because it takes many less turns on the black canisters then the blue canisters to accomplish the same spring tension change. I think I picked this up from Andrew or Chris, but this is one of the great things about the PRO arm--it's versatility.

Hope you are sunny and warm in South Florida, it's been cold and rainy on this Michigan job.

-Matt



yeah that's a good point Matt! less turns...always good!

but what about the feel of black against blue canisters? Is it just me or do they feel a bit different...not complaining...they are both great and the PRO is the best arm out there but just think that the blues feel more "floaty" than the blacks...?

Anyways,

thanks for the responses gents,

Jerry
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#6 Mike McGowan SOC

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Posted 16 May 2010 - 10:26 PM

interesting. your looking to make bigger adjustments more quickly. my goal is to do more fine adjustment more quickly. of course, with the pro arm you can basically make a really fine adjustment with the black spring by just making a slight turn.............. ill have to mess around with that. on topic, the idea either way is to have the easiest access to the springs you use most.

@jerry........ i dont even think i notice a difference but ill play with them tomorrow on set and see what i notice.
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#7 Eric Fletcher S.O.C.

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Posted 16 May 2010 - 10:43 PM

Actually since its two springs in series its the same number of turns no matter which canister you adjust.
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#8 Mike McGowan SOC

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Posted 18 May 2010 - 08:25 AM

humm........ so your saying that if i have one black and one blue in each section it doesn't matter if i add one turn to a black or one turn to a blue, it would end up changing the weight the exact same amount? that doesn't seem possible. i understand that you only need to adjust one spring per section but the black spring adds more tension with less turns than a blue spring does, no?
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#9 Iain Baird

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Posted 18 May 2010 - 08:47 AM

I think the reasoning is that although the blue and black are of different strengths ONE turn on each is the same. Two Blues can range from 13-24 pounds while two Blacks range from 24-34 pounds. By this math each cannister has about a five pound lift range be it blue or black, so one turn on either should be equal to the other (in fact at 5.5 pounds per cannister Blue may be a little more!!)

Iain
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#10 Eric Fletcher S.O.C.

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Posted 18 May 2010 - 11:39 AM

Yes mike thats the way it works. Cant get past physics and its Hooke's Law that governs spring calculations
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#11 Brian Freesh

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Posted 18 May 2010 - 11:56 AM

I looked up Hooke's law and I almost understand it. I love stuff like that that seems crazy on first glance but actually makes sense. Last night, for the first time since high school chemistry, I witnessed freezing of a liquid due to pressure change. Physics and chemistry blow me away!

Also, totally useless post, apologies.
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#12 Matt Petrosky

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Posted 19 May 2010 - 09:43 AM

I think the reasoning is that although the blue and black are of different strengths ONE turn on each is the same. Two Blues can range from 13-24 pounds while two Blacks range from 24-34 pounds. By this math each cannister has about a five pound lift range be it blue or black, so one turn on either should be equal to the other (in fact at 5.5 pounds per cannister Blue may be a little more!!)

Iain



Yes mike thats the way it works. Cant get past physics and its Hooke's Law that governs spring calculations



Eric and those of you with strong physics backgrounds, please help me understand this a bit better.
Let me see if I've got this straight:

For simplicity's sake, let's say that the blue and the black canisters can each be adjusted to within 5 pounds of their respective lift range. For simplicity's sake, let's also say that the blue and black canisters each require 100 full turns to adjust from their respective lower limit to their respective higher limit. Then as the blue canister is turned 20 times, it's tension will increase/decrease 1 pound. And as the black canister is turned 20 times, it's tension will increase/decrease 1 pound. Right?

But what throws me off is this, the blue and the black canisters do NOT require the same 100 turns (again, a round number for simplicity's sake) to adjust within their respective ranges. In fact, the black canister only requires/allows just a bit more then HALF the number of turns. So if the black canister requires 50 turns to adjust within it's 5 pound range, and the blue canister requires 100 turns, then it wouldn't it take less turns to equal the same range adjustment from a black canister?

Now I am basing my simplified number of turns math on the fact that the blue canisters allow me to move the spring and it's white marker within the full (approx.) 2" adjustment window. The black canisters do not. They only allow adjustments within of a portion of the adjustment window scale before they hit their end-stops. Now I suppose that the blue and black canisters could have different pitched threads on the screws that drive the adjustments. This could make one turn on one equal one turn on the other, while the actual compression range is not 1:1, blue to black. I'll forward this to George and see if I we can get an answer about the adjustment drive screws.

Thanks in advance for any clarification anyone can offer me.

-Matt
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#13 Brian Freesh

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Posted 19 May 2010 - 11:27 AM

IF I understand correctly, because they are in series they act as one spring. Lower the lift capacity on one spring and the other spring will balance the difference every time. If the TOTAL lift capacity of two springs is 10-20 lbs, it won't matter if one spring capacity is 2-4 lbs and the other is 8-16 lbs or if they are both 5-10 lbs. They always act together for the total lift range.
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#14 Eric Fletcher S.O.C.

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Posted 19 May 2010 - 11:40 AM

IF I understand correctly, because they are in series they act as one spring. Lower the lift capacity on one spring and the other spring will balance the difference every time. If the TOTAL lift capacity of two springs is 10-20 lbs, it won't matter if one spring capacity is 2-4 lbs and the other is 8-16 lbs or if they are both 5-10 lbs. They always act together for the total lift range.



EXACTLY!!!! As far as the arm function works the two springs are one since they are in series.

For example purposes let's call the blue a 50lbs/in spring and the black a 100lbs/in spring. Two blues would equal 100lbs/in two blacks 200lbs/in and a black and blue would be 150lbs/in

Adjust either spring in the stack and it will have the same total effect no matter if it's the softer or the stiffer of the two springs. All that changes is the adjustment delta depending on the spring combo's used
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#15 Matt Petrosky

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Posted 19 May 2010 - 12:27 PM

IF I understand correctly, because they are in series they act as one spring. Lower the lift capacity on one spring and the other spring will balance the difference every time. If the TOTAL lift capacity of two springs is 10-20 lbs, it won't matter if one spring capacity is 2-4 lbs and the other is 8-16 lbs or if they are both 5-10 lbs. They always act together for the total lift range.



EXACTLY!!!! As far as the arm function works the two springs are one since they are in series.

For example purposes let's call the blue a 50lbs/in spring and the black a 100lbs/in spring. Two blues would equal 100lbs/in two blacks 200lbs/in and a black and blue would be 150lbs/in

Adjust either spring in the stack and it will have the same total effect no matter if it's the softer or the stiffer of the two springs. All that changes is the adjustment delta depending on the spring combo's used


Okay, thanks guys, this makes sense.

But I don't understand how it answers my original question:

If I insert a t-handle allen into a black spring canister in my arm, and I rotate it 360 degrees clockwise, does that action have the same effect, more effect, or less effect then if I rotate a t-handle in a blue canister 360 degrees clockwise in the same arm?

Thanks,
Matt
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